Please try the sample script to remove the second entry of the legend:
int n = 2;
string strNewLegend$ = legend.text$;
string strRemove$ = strNewLegend.Token(n, CRLF)$;
int s = strNewLegend.Find(strRemove$);
int l = strRemove.len();
strNewLegend.delete(s,l+2);
legend.text$ = %(strNewLegend$);
James